1. Field of the Invention
The present invention relates generally to an image photographing device for photographing and recording and storing image data. More particularly, the present invention relates to an iris diaphragm, a diaphragm driving device, and a camera unit including the same, and a diaphragm control method.
2. Description of the Related Art
A camcorder is a representative example of an image data recording and reproducing device, and is widely used today for photographing moving images and still images. A camcorder includes a camera unit, a signal conversion unit, a deck for recording and reproducing photographed images, and a display unit. The camcorder usually uses a cassette tape as a recording medium to record photographed image data. Also, in recent years, attention has been focused on a small-sized, light-weight image recording and reproducing device using a compact-sized recording medium, such as a hard disk drive. The small-sized, light-weight device was made possible because a deck is not included in the image recording and reproducing device using a hard disk drive.
The camera unit and a lens barrel with a focusing lens and a zoom lens are packed in a module and are installed inside the main body of a product. The focusing lens and the zoom lens are driven by a motor installed in the lens barrel.
The lens barrel includes a lens shutter for adjusting the amount of incident radiation. In effect, a plurality of motor-driven shutter members adjust the amount of incident light passing through the lens while moving.
According to the above configuration, in addition to the lens motor, a plurality of motors are arranged outside of the lens barrel. Theses types of motors are disadvantages for reducing the size of the camera unit.
Moreover, as the motor is mounted on the outer side of the cylindrical lens barrel, the lens barrel has the angular outer configuration only. Therefore, there is a limit in the designing of the lens barrel.
A Neutral Density (ND) filter is also housed in the lens barrel. The ND filter reduces the amount of incident light that passes through the lens, and suppresses an occurrence of diffraction where resolution is noticeably reduced at a high brightness level. As a result, resolution is much improved.
However, a problem arises as the ND filter is bonded or coupled to the lens shutter and moves with the lens shutter as one body. Despite the changes of the diaphragm of the lens or the opening degree of the lens shutter, a part of the light path is always blocked by the ND filter. Although this fact does not have a great impact on the resolution at high brightness, it greatly reduces resolution at low brightness so the amount of light passing through the lens is very low.